Nicholas "Oz" Ozeransky (Matthew Perry) keeps a SIG-Sauer P228 pistol in his house for protection and later gives it to Jimmy (Bruce Willis), who uses it for a good duration of the film.
Towards the end of the film, Jill tries to convince Lazlo (Kevin Pollak) that she is working for him, so she uses her Smith & Wesson 5906 to shoot Jimmy. Later, when Jimmy is seen unharmed, they explain to Oz how the first round was live, so she could shoot a lamp to convince him it was real, and then the rest were blanks. One cannot simply switch from live rounds to blanks since blanks don't have enough pressure to cycle a real gun and a blank converted gun can't handle a live round.
NEF Pardner
When Jill tells Jimmy about her failed hit, we see how she brings an H&R-made NEF Pardner shotgun. Her hit falls out of a window before she can use it.
Glock 17
Lazlo Gogolak (Kevin Pollak) uses a Glock 17 2nd Generation to execute two men in the trunk of a car telling them to tell everyone he is back in town. His son Strabo then asks how they can tell anyone he's in town if they are dead. He gets backhanded for correcting him.
Mossberg 500
Jimmy and Jill keep a sawed-off Mossberg 500 shotgun with raised barrel ribbing, a saddle-mount shell holder, and a pistol grip hidden in their house. Jill picks it up and fires it at Lazlo's men when they attack their house.
M16A2
When Oz first arrives at Jimmy's secret house in Mexico, he is met by gunfire from Jimmy who is wielding an M16A2 assault rifle. Oz also keeps a few M16A2 rifles in his house armory.
Walther PPK/S
When Strabo (Frank Collison) goes to Oz's for a dentist appointment, he tries to pulls out a Walther PPK/S to kill Oz, but Oz leaves him under anesthetic for too long and knocks him out.
Remington 700 AICS
Julie "Jules" Figueora (Tasha Smith) uses an Remington 700 AICS fitted with a five round magazine to take shots at Jimmy, Jill, and Oz at Oz's house and ends up killing Strabo with it when he gets shot in the foot while hiding in the trunk. Despite being a bolt-action rifle, the gun is shown capable of several rapid shots like a semi-automatic.
Heckler & Koch USP
Julie draws a Heckler & Koch USP chambered in 9mm on Oz after she knocks out Jimmy and reveals she was Frankie Figs' sister. Jimmy later gets his hands on it and uses it to take out the last of the thugs.
Smith & Wesson Model 19
Strabo keeps a four-inch Smith & Wesson Model 19 revolver as his sidearm in the film, losing it when Jimmy takes him hostage.
Beretta 92FS
One of Lazlo's thugs, Zevo (Johnny Messner), uses a Beretta 92FS as his sidearm in the film. When Jimmy kills Zevo, Jill uses the Beretta to shoot Lazlo in the foot. The police responding soon after are also armed with Berettas.
Smith & Wesson Model 60
One of Lazlo's thugs uses a Smith & Wesson Model 60, the stainless model of the Smith & Wesson Model 36 as his sidearm in the film. After he is killed, Jill uses his Model 60 for a brief duration. When Lazlo learns it was Julie who killed Strabo, he forces Jill's arm in her direction and shoots her with the gun.
Cobray M11/9
One of Lazlo's thugs uses a Cobray M11/9 to shoot at Jimmy's house in Mexico.
Micro Uzi
One of Lazlo's thugs uses a Micro Uzi to shoot at Jimmy's house in Mexico.
Lazlo's Pistol Rack
At the start of the film, a rack is seen behind Lazlo with pistols including a Walther P38 and various Smith & Wesson revolvers.
Sawed-off Shotgun
At the start of the film, Lazlo's guard is seen with a Sawed-off Shotgun.
Oz's Arsenal
Oz keeps a vast array of weaponry in his house. Some of them have already been listed above. These weapons include: